This invention generally pertains to an injection molding apparatus. More specifically, the present invention relates to a gas assisted injection molding apparatus which utilizes a pin-in-sleeve device to direct a gas into a mold cavity.
Gas assisted injection molding has by now become quite popular for its many advantages. These advantages are set forth in, e.g., U.S. Pat. Nos. 4,905,901 dated Mar. 6, 1990; 5,151,278 dated Sep. 29, 1992; 5,164,200 dated Nov. 17, 1992; 5,174,932 dated Dec. 29, 1992 and 5,256,047 dated Oct. 26, 1993. The disclosure of each of these patents is specifically incorporated hereinto in its entirety.
For a pin-in-sleeve arrangement, a pin is positioned in a sleeve such that an annular fluid flow passage is defined between the pin and the sleeve. Pin-in-sleeve arrangements are employed for feeding gas into a mold cavity either through a nozzle, which regulates the flow of plastic into the mold cavity, or spaced from such nozzle. When the pin-in-sleeve device is spaced from the nozzle, the gas is directed into the article. This is termed in-article gas assisted injection molding.
When an in-article gas assisted injection molding device is employed, it is desirable to allow a quick change out of a gas pin of the device. The quick change out feature reduces down time for a molder who would normally have to pull the mold out of the injection molding machine to replace a pin that has become plugged with resin.
Resin plugging of gas injection pins has always been the main problem of gas assisted injection molding. There have been many complicated devices invented to overcome this problem. However, none of these devices have really worked satisfactorily. The pin-in-sleeve design for in-article gas assisted injection molding disclosed herein recognizes the fact that pins without check valves always will plug sooner or later.
Accordingly, it has been considered desirable to develop a new and improved pin-in-sleeve device for in-article gas assisted injection molding which would overcome the foregoing difficulties and others while providing better and more advantageous overall results.